In order to produce stimulated emission we need a photon which has the same energy as the difference is the lower and upper energy levels in the excited atom. But how exactly the energy of the photon does have to correspond to the energy difference between the levels. Can stimulated emission still occur if the photon has little less or little more? If so, where does the rest of the energy come from or where does the rest of the energy go? Can we get the extra energy from or put the rest in some form of collisional energy? If we have a photon that does not exactly match for the energy of the energy levels will the stimulated emission then be only less probable according to the stimulated emission cross section. Einstein's coefficient for stimulated emission should in this case only be for a photon of the exact energy?